DE4431957A1 - Process for the catalytic gas-phase oxidation of propene to acrolein - Google Patents

Abstract

A process for the catalytic gas-phase oxidation of propene to acrolein in a multiple contact tube fixed-bed reactor, with only one heat transfer medium being circulated through the space surrounding the contact tubes, at elevated temperature over catalytically active multimetal oxides at a propene conversion on a single pass of >/= 90 mol% and a selectivity of acrolein formation of >/= 85 mol%, in which the heat exchange medium on the one hand is passed longitudinally, viewed over the reaction vessel, to the contact tubes in cocurrent to the reaction gas mixture through the multiple contact tube fixed-bed reactor and, on the other hand, has, within the reaction vessel, due to a successive arrangement, along the contact tubes, of deflecting discs which leave open cross-sections free, a superposed crossflow in such a way that, in longitudinal section through the contact tube bundle, a meander-like flow of the heat exchange medium results and the flow velocity of the circulated heat exchange medium is here set in such a way that the temperature of the heat exchange medium rises by from 2 to 10 DEG C from the inlet point to the reactor to the outlet point from the reactor.

Description

The present invention relates to a new method for Catalytic gas phase oxidation of propene to acrolein in one Multi-contact tube fixed bed reactor through which the contact tubes surrounding space only a heat exchange medium circuit is passed at elevated temperature to catalytically active Multimetal oxides with a propene turnover with simple Passage of 90 mol% and selectivity of acrolein imagination of 85 mol%.

The catalytic gas phase oxidation of propene to acrolein is generally known and in particular as the first oxidation stage at the production of acrylic acid by two-stage catalytic Gas phase oxidation of propene in two series Reaction stages of importance (see, for example, DE-A 30 02 829). Acrylic Acid is an important monomer, either as such or in form its alkyl ester for the production of z. B. geei as adhesives gneten polymers is used.

The gas phase oxidation of propene to acrolein is highly exo therm, which is why it is due to a variety of possible parallel or subsequent reactions with a view to being as selective as possible Conversion of propene to acrolein and for a manageable Performing the gas phase oxidation is necessary at all, the course of the reaction temperature to a certain extent Taxes.

A very commonly used way of directing the free heat of reaction is the reactants Oxygen and acrolein with inert gases such as N₂, carbon oxides such as CO₂ and CO, hydrocarbons, recycled reaction gases and / or dilute water vapor using Dilution gases with the highest possible molar heat capacity is particularly advantageous (cf. EP-B 253 409).

Another generally used method for controlling the Reaction temperature is the catalytic gas phases Oxidation of propene to acrolein in a multi-contact tube solid perform bed reactor. Such reactors correspond in their Type the shell and tube heat exchangers. That is, their usual design consists of a, usually cylindrical, container, in which corresponds to a plurality of tubes (a tube bundle)  the cooling tubes of a jacket-tube heat exchanger in the usual way wise vertical arrangement is housed. These contact tubes, each one a fixed bed arrangement of the corresponding one contains catalytically active multi-metal oxide, are with their Ends sealed in tube sheets and each end in a upper or lower end of the hood connected to the container. over these hoods become the reaction flowing through the contact tubes gas mixture supplied or removed, so that each contact tube one elongated reaction unit zone corresponds.

Furthermore, heat is generated by the space surrounding the contact tubes exchange medium directed to manage the process heat. To the heat exchange medium, e.g. B. in external heat exchangers, back to their original Brought to temperature before returning to the reaction vessel occur (see e.g. DE-A 30 242 468).

Steps along the contact tubes on different (several) High heat exchange medium in the reactor, so here from the application of several heat exchange medium circuits be spoken. If the heat exchange medium occurs only at one level, here is a heat exchange middle circuit spoken, even if this circuit is not with one, but for the sake of convenience with several Pumps is operated.

The contact tubes are usually made of ferritic steel and typically have a wall thickness of 1 to 3 mm on. Their inner diameter is usually 20 to 30 mm. The The pipe length normally extends to a few meters (typical is a contact tube length in the range of 2 to 4 mm). Application technically expedient is that accommodated in the container Number of contact tubes to at least 5000, preferably to at least 10,000. Often the number in the reaction is Contact housings 15,000 to 30,000 housed bundle reactors with a number above 40,000 Contact tubes are rather the exception. Inside the container the contact tubes are normally distributed homogeneously, the distribution is expediently chosen so that the distance the central inner axes of cones closest to each other tact tubes (the so-called contact tube pitch) 35 to 45 mm be carries (see e.g. EP-B 468 290).

Fluid temperatures are particularly suitable as heat exchangers media. The use of melts is particularly favorable of salts such as potassium nitrate, potassium nitrite, sodium nitrite and / or  Sodium nitrate, or of low melting metals like Sodium, mercury and alloys of various metals.

From DE-C 25 13 405 it is known for propene sales at fold of at least 90 mol% the course of the reak tion temperature of the catalytic gas phase oxidation of propene to acrolein in a multi-contact tube fixed bed reactor at kata to control lytically active oxides so that the contact pipes around the room a molten salt circulating at 330 ° C liert and the reaction gas mixture preheated to this temperature is fed.

DE-A 30 42 468 and DE-A 30 02 829 recommend for smoothing the temperature distribution within the catalyst beds Heat exchange medium and the reaction gas mixture in cocurrent through the multi-contact tube fixed bed reactor. Here recommends the state of the art to get as many contact tubes as possible Participate evenly in the reaction process in a balance right section of the reactor (perpendicular to the reactor axis) one to achieve as homogeneous a temperature as possible of the heat exchange medium ben (e.g. DE-PS 16 01 162). The state of the art also recommends Technology, the heat exchange medium as quickly as possible through the reak to conduct gate, so the released heat of reaction as possible dissipate effectively. It is recommended that the heat exchange medium be so in a circle that the temperature difference of the inserted heat exchange medium between the entry and exit points disappearing from the reactor as much as possible.

A general problem of catalytic gas phase oxidation of There is propene to acrolein in the multi-contact tube fixed bed reactor in that the reaction temperature is in the longitudinal direction of a contact tube a maximum, a so-called hot spot, goes through. On the one hand, this diminishes in this contact tube cut the life of the catalyst and affected on the other hand the selectivity of acrolein formation.

Various countermeasures to overcome the above some are already recommended in the prior art. A before Impact consists in reducing the diameter of the contact tubes, so the heat dissipation per unit volume of the catalytic converter increase tors. The disadvantage of this method, however, is that it the number required for a particular production output catalyst-filled catalyst tubes necessarily increased, which both the manufacturing costs of the reactor and the Filling and emptying the catalyst tubes with catalyst required duration increases.  

Another proposed procedure is training to suppress the hotspots by trying to Volume-specific activity of the catalytic feed along the contact tubes vary. However, this procedure requires inevitably use either at least two Catalysts of different activity or shared use of inert material. This procedure also complicates the filling of the contact tubes (an overview contains the various countermeasures proposed for example, DE-PS 28 30 765). Another obvious one One way to reduce hot spot formation is to Reduce propene load on the reactor. This measure min changes at the same time the space-time yield of the desired Product.

DE-A 40 23 239 recommends catalytic gas phase oxidation from propene to acrolein so that the reaction temperature temperature in the flow direction along the contact tubes from the entry of the the reactant-containing reaction gases into the contact tubes to achieve a propene conversion of 30 to 70 mol% 360 up to 420 ° C, then until reaching a Turnover of propylene from 80 to 90 mol% to 360 to 300 ° C adjusted and then until the reaction gas mixture emerges is kept from the contact tubes at 330 to 390 ° C. Disadvantageous However, this procedure is that the hiring of a such temperature profile the application of more than one Heat exchange medium circuit required.

DE-A 22 01 528 covers for exothermic catalytic multiple contact Pipe fixed bed oxidations in addition to the possibility of heat loss means of exchange in a simple manner essentially directly along the contact tubes also have the ability to guide these longitudinally only considered the entire reaction container to realize and this longitudinal flow within the reak tion container by one along the contact tubes leaving the following arrangement of passage cross sections free Deflection discs to overlap a cross flow so that in the longitudinal cut a meandering flow through the tube bundle of the heat exchange medium results. Include this suggestion also DE-PS 28 30 765, DE-A 22 31 557 and DE-A 23 10 517.

From Trans I chem. E, Vol. 71, Part B, August 1993, pp. 208 to 214, it is known that in exothermic catalytic contact tube fixed bed oxidation confusing indirect interaction between the heat emitted by the individual contact tubes take place, which is why the local location of the hotspot and its  The extent in the individual contact tubes is usually the same is different and difficult to assess with foresight.

In view of this state of the art, the task of present invention in a new method for kata lytic gas phase oxidation of propene to acrolein in one Multi-contact tube fixed bed reactor through which the contact tubes surrounding space only a heat exchange medium circuit is passed at elevated temperature to catalytically active To provide multimetal oxides for a given A reaction mixture containing propene with a given catalyst loading as well as a predefined propene load Propene conversion (90 mol% in a single pass) and a given selectivity (85 mol%) of the acrolein formation (i.e. a given space-time yield of acrolein) in the simplest and cheapest possible under training can deliver reduced hot spot temperatures.

Accordingly, there has been a process for gas phase catalytic oxidation from propene to acrolein in a multi-contact tube fixed bed reactor, through the space surrounding the contact tubes only a Heat exchange medium circuit is directed at increased Temperature of catalytically active multimetal oxides with a Conversion of the propene with a single pass of 90 mol% and a selectivity of acrolein formation of 85 mol% was found, which is characterized in that the heat exchange medium on the one hand viewed along the reaction vessel along the Contact tubes in cocurrent to the reaction gas mixture through the Multi-contact tube fixed bed reactor conducts and on the other hand within of the reaction vessel through one along the contact tubes leave any other arrangement of passage cross-sections free the deflection disks superimposed a cross flow that in the longitudinal cut a meandering flow through the tube bundle of the heat exchange medium results, with the proviso that the Flow rate of the heat build-up circulated is measured so that the temperature of the heat medium of exchange from the point of entry into the reactor to Exit point from the reactor by 2 to 10 ° C, preferably around 3 to 6 ° C, increases.

DE-PS 16 01 162 advises in column 2 of such an out leadership form, since with it no sufficiently uniform pipe to reach temperatures across the reactor cross-section be.  

The temperature at which the heat exchange medium enters the reactor is chosen in a manner known per se so that given catalyst feed and propene Burden that to achieve the required propene turnover as well the required acrolein selectivity required reaction temperature profile. The reaction usually lies temperatures of such a profile when using the for this Purpose known to use molybdenum, bismuth and iron in multimetal oxide catalysts containing oxidic form at 300 up to 450 ° C. Preferred inlet temperatures are accordingly of the heat exchange medium at 280 to 380 ° C. So appropriate Nete multimetal oxide catalysts can for example US-A 3 825 600, US-A 3 649 930 and US-A 4 339 355 become. Furthermore, the multimetal are particularly suitable oxide compositions of DE-A 42 20 859.

A variety of suitable multimetal oxide catalysts under the general formula I

Mo₁₂ Bi _a Fe _b X¹ _c X² _d X³ _e X⁴ _f O _n (I),

in which the variables have the following meaning:
x¹ nickel and / or cobalt,
x² thallium, an alkali metal and / or an alkaline earth metal,
x³ phosphate, arsenic, boron, antimony, tin, cerium, lead and / or tungsten,
x⁴ silicon, aluminum, titanium and / or zirconium,
a 0.5 to 5,
b 0.01 to 3,
c 3 to 10,
d 0.02 to 2,
e 0 to 5,
f 0 to 10 and
n is a number that is determined by the valency and frequency of the elements other than oxygen,
subsume.

They are available in a manner known per se (see, for example, the earlier application DE-A 40 23 239) and are usually in Substance formed into balls, rings or cylinders or else in the form of coated catalysts, d. H. with the active mass coated preformed, inert carrier bodies used. Of course, they can also be used in powder form Catalysts are applied.  

Oxygen is used as the oxidizing agent. Is considered inert Dilution gas N₂ selected, the use of air proves particularly advantageous as an oxygen source.

As a rule, with a propene: Oxygen: indifferent Gases (including water vapor) volume (Nl) ratio of 1: (1.0 to 3.0) :( 5 to 25), preferably (1: (1.7 to 2.3): (10 to 15) worked. The reaction pressure is usually in the Range from 1 to 3 bar and the total space load is before preferably 1500 to 2500 Nl / l / h.

In the process according to the invention, no pure acrolein is used but obtained a mixture, the secondary components of which Acrolein can be separated in a manner known per se. At a use of acrolein for the production of acrylic acid through two-stage catalytic gas phase oxidation of propene the acrolein-containing reaction gases are usually without Separation of the secondary component in the second oxidation stage transferred.

With regard to contact tube material, dimensioning, number, Pipe division and possible heat exchange medium applies to that The method according to the invention in the context of the assessment of State of the art. As a preferred heat exchange medium According to the invention, a salt melt consisting of 60% by weight Potassium nitrate (KNO₃) and 40 wt .-% sodium nitrite (NaNO₂) set.

To generate the cross flow required according to the invention For example, an arrangement of deflection disks can be used that are alternately on opposite sides of the Leave an average cross section of the reactor vessel free (cf. e.g. B. DE-AS 10 39 040). With increasing performance of the Reactor, because of the large number of contact tubes too the ratio of the diameter to the length of the reaction vessel is correspondingly large, but an arrangement of deflection preferred slices that alternate in the middle and on her outer edge (the attachment of such deflection disks can e.g. a rod mounted vertically in the reactor center) leave a passage cross section free (additional feature a), see above that the heat exchange medium one after the other from the outside is routed inside and inside out. With advantage one essentially arranged in a ring-shaped tube bundle (whereby essentially each contact tube advantageously six equidistant neighbors) with a free central space turn, the diameter of the free central space about 10 to 30% of the inside diameter of the reactor is (additional note  times b). The distance of the outermost contact tubes the container wall will normally be a few centimeters. Furthermore, the contact tubes are preferably on the deflection disks not sealed. Rather, be between the contact tubes and the deflecting washers (gap width in usually <1 mm) so that the cross flow velocity speed of the heat exchange medium within one between two successive deflection disks located con if possible is constant (additional feature c). In connection with different Distances of the deflection disks can also be achieved with advantage Chen that the temperature differences (if possible 3 ° C) and the Pressure losses in a horizontal section within a zone be restricted (additional feature d). Furthermore, it proves According to the invention as favorable if the entry and exit of the Heat exchange medium over at both ends of the tank attached ring lines with the same over the entire circumference distributed windows takes place, the window openings so ge stalten that the same through each window per unit of time Amount of heat exchange medium occurs (additional feature e) to a radial supply and discharge of the heat output as uniform as possible guarantee means of exchange (see. DE-A 16 01 162).

It is also advantageous according to the invention if on a Sales volume of 20 to 50 mol% of propene converted, preferably 20 to 40 mol%, the reactor a subset of the heat exchange is removed (e.g. via another ring line to the Dissipate), preferably 30 to 70%, particularly preferred 40 to 60% of the total amount of heat exchange medium supplied is (additional feature f). Furthermore, the reaction gas mixture the catalyst feed preferably to the entry temperature temperature of the heat exchange medium supplied preheated (add feature g). This can be done in a simple manner by flow an inert material at an appropriate temperature Realize the filling.

In the case of method variants which are particularly advantageous according to the invention as many of the additional features a to g as possible are fulfilled simultaneously. All additional features a to g simultaneously are particularly preferred fills. It is assumed on this side that in particular the latter procedure, a temperature profile in the Contact tube wall is achieved along a single contact tube, where the temperature of the contact tube wall up to a pro pen conversion of 20 to 50 mol% is essentially constant and then grows by 2 to 10 ° C to the end of the pipe. It will this side also assumed that in this procedure in the aforementioned sales area also across the reactor cross  cut essentially uniform wall temperatures of the Contact tubes are available.

In general one will try to use the number of Restrict baffles. Appropriate from an application point of view this number is 3 to 9. One for performing the particularly advantageous method variant according to the invention suitable reactor type is shown in FIG. 1 of DE-AS 22 01 528.

Of course, the procedure according to the invention for Reduction of the hot spot temperature for a given space-time Yield with the methods listed in the prior art proposals can be used in combination.

Turnover U and selectivity S are as follows in this document Are defined,

and related to simple passage.

Examples A. Process for the catalytic gas phase oxidation of propene Acrolein in a multi-contact tube fixed bed reactor in which the heat exchange medium is essentially direct is led lengthways to the contact tubes (comparative examples) I. Description of the general process conditions

Heat exchange medium used: molten salt, consisting of 50% by weight of potassium nitrate and 50% by weight of sodium nitrite;
Contact tube material: ferritic steel;
Dimensions of the contact tubes:
3 200 mm length;
25 mm inner diameter;
30 mm outer diameter (wall thickness: 2.5 mm).
Number of contact tubes in the tube bundle: 15 700;
Reactor:
Cylindrical container with an inside diameter of 5000 mm;
Homogeneous distribution of the contact tubes over the entire cross-section with a contact tube pitch of 38 mm.

The ends of the contact tubes were in contact tube floors with a thickness of 100 mm were sealed and opened with their openings in one at the top and one at the bottom End hood connected to the container.

Feeding the heat exchange medium to the tube bundle:
Via an annular channel attached to the reactor vessel (reactor jacket). Window inflow in the radial direction to the tube bundle attached over the circumference of the reactor jacket.

25 mm below the upper tube sheet and 25 mm above of the lower tube sheet were 10 mm thick dividers attached across the entire cross section extended. Between the dividers and the contact tubes existed permeable gaps.

The salt melt occurred between the lower tube plate and the lower divider into the tube bundle and ver shared over the column on the reactor cross-section and then rose parallel to the contact tubes. The molten salt flowed when the upper partition was reached through the gap between the divider and the con clock tubes through and then flowed into the space between the upper partition and the upper tube plate radially to outer tube circle and collected through window through step in an upper ring channel around the reactor jacket and after cooling to the original entry temperature by a pump into the lower ring channel pressed. The gap widths were selected in accordance with the DE-PS 16 01 162 and DE-AS 16 75 501 so that there is for everyone Current threads from the lower to the upper ring channel the same hydraulic resistance resulted.

Contact tube loading:
Shell catalyst according to Example 1c), 1 of DE-OS 29 09 597
Structure of the feed (from bottom to top):
500 m bulk height bare catalyst supports,
1000 mm coated catalyst with 37% by weight active mass fraction,
1700 mm coated catalyst with 42% by weight of active mass.

Reaction gas mixture load: 40 960 Nm³ / h.

Composition of the reaction gas mixture:

5.4% by volume of propene,
10.5% by volume oxygen,
1.7 vol.% CO _x ,
80.8 vol.% N₂,
1.6 vol .-% H₂O.

Specified implementation data:

U = 95 mol%, S = 90 mol%,

Space-time yield: 202 kg acrolein / m³h.

II. Results

The above given specifications could under the following Conditions are realized:

The hot spot temperature was measured on 5 contact tubes determined that in the tube bundle equidistant from the very outside radially to the inside were selected. The specified temperature gives the highest determined Hotspot value again.

Countercurrent flow of molten salt and reaction gas mixture obviously causes the unfavorable Hotspot temperatures.  

With direct current routing, the hot spot conditions with increasing pump power, d. H. increasingly disappearing the temperature difference between entry and Outlet temperature of the molten salt is more favorable.

There was no stable continuous under conditions d) Long-term operation of the reactor is possible.

B) Process for the catalytic gas phase oxidation of propene Acrolein in a multi-contact tube fixed bed reactor in which the heat exchange medium in longitudinal section through the contact tube bundle is meandering I. Description of the general process conditions

Heat exchange material used: like AI;
Material and dimensions of the contact tubes: like AI;
Number of contact tubes in the tube bundle: 25 500;

Reactor:
Cylindrical container with a diameter of 6800 mm. Ring-shaped tube bundle with a free central space.
Diameter of the central free space: 1000 mm distance of the outermost contact tubes to the tank wall: 150 mm.
Homogeneous contact tube distribution in the tube bundle (6 equidistant neighboring tubes per contact tube), contact tube pitch: 38 mm.

The ends of the contact tubes were in contact tube floors with a thickness of 125 mm were sealed and opened with their openings in one at the top and one at the bottom End hood connected to the container.

Feeding the heat exchange medium to the tube bundle:
The tube bundle was divided into four equidistant (each 730 mm) longitudinal sections (zones) by three deflecting disks (thickness 10 mm each) successively attached along the same along the contact tube bases.

The bottom and the top deflection ring showed ring geometry, with the inner ring diameter 1000 mm was and the outer ring diameter up to Sealing the container wall. The contact tubes were not sealingly attached to the deflection disks. Rather, the gap width was <0.5 mm Leave the gap so that the cross flow velocity the molten salt within a zone as constant as possible was.

The middle pulley was circular and extended yourself to the most outermost contact tubes of the tube bundle.

The circulation of the molten salt was by two salt pumps, each of which is a tube bundle long half supplied.

The pumps pressed the molten salt around you Reactor jacket attached below the ring channel, which holds the salt melt distributed over the circumference of the container. By im Windows located in the reactor jacket reached the salt melt in the lowest longitudinal section to form the tube bundle. The molten salt then flowed to the specification of the baffle plates following in sequence

• - from the outside to the inside,
• - from the inside to the outside,
• - from the outside to the inside,
• - from the inside to the outside,

essentially meandering, viewed over the container tet, from bottom to top. By in the top longitudinal section cut windows around the perimeter of the container the molten salt collected in an upper one around the Reactor jacket attached ring channel and was after Cooling down to the original inlet temperature the pumps are pushed back into the lower ring channel.

Contact tube feed, structure of the feed, composition of the reaction mixture and given implementation data: as AI
The load with reaction gas mixture: 66 530 Nm³ / h.

II. Results

The given implementation data (turnover, selectivity, Space-time yield) could under the following conditions conditions can be realized:

The hot spot temperature was measured on 5 contact tubes determined that in the tube bundle equidistant from the very outside radially to the inside were selected. The specified temperature gives the highest determined Hotspot value again.

Countercurrent flow of. Viewed through the reactor Salt melt and reaction gas mixture are also necessary here obviously the worst hot spot temperatures.

The hotspot behavior takes place in a surprising manner here in contrast to A) with decreasing pumping power (increasing difference between entry and exit temperature of the heat exchange medium), however, a minimum. The inhomogeneities decrease with decreasing pump power in the temperature profile of the reactor (horizontal section) however, for which reason a Δ of 3 to 6 ° C between the inlet and outlet temperature of the heat output medium of exchange is preferred.

This surprising finding is evident on it attributed to that by the cross flow component improved heat exchange as well as through the reduced Inlet temperature of the heat exchange medium increased Cooling effect in the range of below 50 mol% Propene sales improved the hot spot behavior and the  associated decrease in the space Time yield of acrolein due to heat toning temperature increase in the range of Propene sales above 50 mol% in surprising Way can be balanced again. A foundation for this result it should be that the heat transfer coefficient on the heat transfer side of the reaction tubes surprisingly obvious with decreasing pump power does not decrease to the same extent as this.

A further improvement is therefore possible in that one implemented at a turnover of 20 to 50 mol% Propene a subset, preferably 30 to 70 mol% of the Inlet amount, the heat exchange medium takes. This requires an even better relative cooling and club the temperature across the reactor cross section in Area of low sales and at the same time a stronger one relative temperature increase in the area of high sales.

At a molten salt inlet temperature of 335 ° C and a reduction in the pumped salt melt from 5400 m³ / h to 2700 m³ / h (partial quantity removed = 50%) at the level of the first (propene conversion = approx. 30 mol%) Deflection disc (throttle valve) results under otherwise same conditions as listed under B, a hot point temperature of 404 ° C at an outlet temperature of 340 ° C. At the same time, such a process improves the homogeneity of the temperature profile of the reak tors (horizontal section) and the homogeneity of the position the hotspots in the individual contact tubes. A decreasing pumping power is equivalent to a considerable cost reduction.

Otherwise, the result according to the invention opens up the Option, either with a given space-time yield a longer stand due to the more favorable hot spot location time to reach the catalyst feed, or at predetermined service life by increasing the load to achieve increased space-time yield.

Claims (16)

1. A process for the catalytic gas phase oxidation of propene to acrolein in a multi-contact tube fixed bed reactor, through the space surrounding the contact tubes only a heat exchange medium circuit is passed, at elevated temperature of catalytically active multimetal oxides with a propene conversion with a single pass of 90 mol% and a selectivity of acrolein formation of 85 mol%, characterized in that the heat exchange medium, viewed on the one hand via the reaction vessel, is passed along to the contact tubes in cocurrent to the reaction gas mixture through the multi-contact tube fixed bed reactor and on the other hand within the reaction vessel through an arrangement of passages which follows one another along the contact tubes cross-sections leaving deflecting disks superimposed on a transverse flow in such a way that a longitudinal section through the contact tube bundle results in a meandering flow of the heat exchange medium, and thereby the str ömungsgeschwindig speed of the circulating heat exchange medium is such that the temperature of the heat exchange medium from the point of entry into the reactor to the point of exit from the reactor increases by 2 to 10 ° C. 2. The method according to claim 1, characterized in that the Temperature rise of the heat exchange medium from the entrance place in the reactor to the point of exit from the reactor increases by 3 to 6 ° C. 3. The method according to claim 1 or 2, characterized in that an arrangement of deflection disks is used, which differ alternating in the middle and at its outer edge a through Leave the cross section free (additional feature a). 4. The method according to claim 1 to 3, characterized in that one has essentially bundles of tubes arranged in a ring applies a free central space. 5. The method according to claim 4, characterized in that the Diameter of the free central space about 10 to 30% of the Reactor inner diameter is (additional feature b).   6. The method according to claim 1 to 5, characterized in that the contact tubes on the deflection disks are not sealed attached, but between contact tubes and deflection plates Leaves column. 7. The method according to claim 6, characterized in that one the gap widths so dimensioned that the cross-flow speed speed of the heat exchange medium within one between two successive deflection disks located zone possible is as constant as possible (additional feature c). 8. The method according to claim 1 to 7, characterized in that one by not equidistant arrangement of the deflection disks Differences in temperature and pressure losses in one horizontal right cut limited within a zone (additional note times d). 9. The method according to claim 1 to 8, characterized in that the entry and exit of the heat exchange medium via to the Ring lines attached to both ends of the reactor vessel with windows spread over the entire circumference takes place, the window openings are designed so that through each window the same amount of time Heat exchange medium occurs (additional feature e). 10. The method according to claim 1 to 9, characterized in that at a turnover of 20 to 50 mol% of propene converted the reactor ent a subset of the heat exchange medium is taken. 11. The method according to claim 10, characterized in that the Withdrawal at a turnover of 20 to 40 mol% converted Propene takes place. 12. The method according to claim 10 or 11, characterized in that the withdrawn portion of the heat exchange medium is 30% up to 70% of the total amount of heat exchange means (additional feature f). 13. The method according to claim 1 to 12, characterized in that that the reaction gas mixture of the catalyst feed preheated the inlet temperature of the heat exchange medium is supplied (additional feature g). 14. The method according to claim 1 to 13, characterized in that the additional features a to g are fulfilled simultaneously.   15. The method according to claim 1 to 14, characterized in that the catalyst feed a molybdenum, bismuth and iron multimetal oxide catalyst containing in oxidic form includes. 16. The method according to claim 1 to 15, characterized in that as a heat exchange medium consisting of a molten salt 60 wt .-% potassium nitrate (KNO₃) and 40 wt .-% sodium nitrite (NaNO₂) is used.